The components based on carbon fiber-reinforced composites are used in different technical areas and commercial sectors, such as the aeronautical and space area, and they are now starting to be used in those applications with important requirements that combine low weight and high mechanical strength, such as some applications in the automotive industry, marine and defense applications, and recreational applications such as bicycles, golf, tennis rackets, and masts.
Carbon fibers in a fabric can be unidirectionally or multidirectionally arranged. There are different ways to combine polymer resin with the dry carbon fiber for the purpose of forming the final composite part, differentiated either by the type of applying force to perform the molding or by the form of applying the heat to activate the resin.
In the case of the composite parts with carbon fiber, prefabricated sheets (prepregs) have typically been used which combine fiber and resin (together with their curing agents) in a sheet manufactured under controlled conditions. These prepregs are subsequently laminated on the mold of the component and are generally cured by means of applying heat and pressure, mainly in an autoclave. The prepregs must be stored in controlled ambient conditions, their use being valid only during a determined storage time.
Due to the high production costs of composite parts using autoclave processes, new manufacturing methods are being developed based on resin injection. These processes do not require such strict storage conditions for the material like those of prepregs in the case of autoclave processes. In these cases, the fiber, which is either dry or slightly mixed with non-activated resin (binder), is manually laminated on the mold with the shape of the composite component. This intermediate element, prior to the final molding of the component, is called a preform. After this step, the mold is closed and the resin is introduced, activating it, for example, by means of applying heat. The resin can be introduced in the mold either by means of vacuum (infusion) or by means of using positive pressure (injection). Like any manual process, it is subjected to possible geometry or composition variations between the different manufactured preforms due to human intervention, which does not assure complete uniformity in the work.
To avoid manual processes, different devices have been designed which allow working in three dimensions (“3D”) using flexible membranes in the preform compacting stage. Such devices are described, for example, in patent applications US-20100007065-A1, JP-2007118598-A, JP-2008230020-A and EP-1808282-A1. Some of the devices described in these documents also allow activating the binder during compaction, but they do so by conventional means, such as by conduction by means of resistors in the mold, by radiation by means of infrared lamps, by convection by means of hot air circulation, etc., which slow the heating process.
With respect to the activation of the binder, binder activation processes by means of resistive heating are known which are based on increasing the temperature by circulating electric current through the carbon fibers, electrical conductors, of the preform.
Thus, patent application WO-01/92002-A2 describes a carbon fiber processing cell where one of the possible preforming technologies which is considered is resistive heating. Patent application WO-03/078141-A1 relates to the processing of thermoplastic composites (not preforms) using resistive heating. Patent application US-20050236098-A1 also considers resistive heating for the material, in this case the resistive circuit being located in the mold. Finally, patent application US-2005140064-A1 describes the manufacture of preforms by means of resistive heating in general. None of these documents refers to how to compact, or how to get the electrodes used for the resistive heating to apply sufficient pressure against the carbon fiber fabric of a preform so that the electrical contact is established without variations that may generate irregularities in the curing and consequently in the final properties of the preform. In the same manner none of these documents is based on using flexible membranes to compact the preform.